Thermodynamics of a protein acylation: activation of Escherichia coli hemolysin toxin.

HlyC, hemolysin-activating lysine-acyltransferase, catalyses the acylation (from acyl-acyl carrier protein [ACP]) of Escherichia coli prohemolysin (proHlyA) on the epsilon-amino groups of specific lysine residues, 564 and 690 of the 1024 amino acid primary structure, to form hemolysin (HlyA). Isothermal titration calorimetry was used to measure the thermodynamic properties of the protein acylation of proHlyA-derived structures, altered by substantial deletions and separation of the acylation sites into two different peptides and site directed mutation analyses of acylation sites. Acylation of proHlyA-derived proteins catalyzed by HlyC was overall an exothermic reaction driven by a negative enthalpy.